Much recent research has concerned development of organic water treatment agents for use in scale or corrosion control. Organic corrosion inhibitors which can reduce reliance on the traditional inorganic inhibitors are particularly sought. Among the organic agents successfully employed for water treatment are numerous organic phosphonates. These compounds may generally be employed without detrimentally interfering with other commercial water treatment additives. Phosphonic acid compounds have also been used in other fields for such purposes as flame retardants, plasticizers, lubricants and surfactants.
U.S. Pat. No. 3,474,133 discloses that certain organo-phosphono-amine oxide compounds can be prepared by oxidizing organo-phosphono amine with a suitable oxidizing agent. For instance ethanol bis(dihydrogen phosphonomethyl) amine can be reacted with H.sub.2 O.sub.2 to yield ethanol bis(dihydrogen phosphonomethyl) amine oxide (i.e. HOCH.sub.2 CH.sub.2 N(O) (CH.sub.2 PO.sub.3 H.sub.2).sub.2); and tris(dihydrogen phosphonomethyl) amine can be reacted with H.sub.2 O.sub.2 to yield tris(dihydrogen phosphonomethyl) amine oxide (i.e. ON(CH.sub.2 PO.sub.3 H.sub.2).sub.3). It is disclosed that the organo-phosphono amine oxides have utility in practically all fields of organic chemistry wherein their acidic or salt and/or amine oxide properties can be utilized; and the various utilities indicated for the compounds in such fields include utility as sequestering or chelating agents, water treating agents, stabilizers for peroxy compounds and corrosion inhibitors. In particular, the acids and water soluble salts of the tris(phosphono lower alkylidene) amine oxides are reported to exhibit the property of being effective sequestering agents for metal ions in alkaline mediums. For example, the penta sodium salt of tris(dihydrogen phosphonomethyl) amine oxide is reported to sequester calcium ions in alkaline media in over a mole per mole basis.
U.S. Pat. No. 3,336,221 to Ralston discloses that compounds having a methylphosphonic acid (or alkali metal or ammonium salts thereof) bonded to a nitrogen atom (e.g. pentasodium amino tri(methyl phosphonate) and phosphonomethyl ethanolamines) are threshold active compounds, useful for inhibiting the precipitation of various scale-forming compounds (e.g. calcium carbonate).
U.S. Pat. No. 3,214,454 to Blaser et al discloses certain acylation products of phosphorous acid (e.g. hydroxyethylidene diphosphonic acid) and use thereof as complex formers for metal ions (e.g. calcium). Delay of calcite precipitation by the use of substoichiometrical amounts of the compounds is disclosed, as is the comparative effectiveness of certain products in preventing scale formation (e.g. in boilers, tubes, etc.).
While as indicated above, various phosphonates have proved useful for particular water treatment applications, many of them nevertheless have important disadvantages when treating water under certain conditions. For example, many phosphonates such as tri(methylphosphonic acid) are not chlorine resistant and thus degrade in the presence of free chlorine which is commonly used as a disinfectant or biocide in many aqueous systems. Other phosphonates including tris(phosphono lower alkylidene) amine oxide compounds such as tris(dihydrogen phosphonomethyl) amine oxide are considered very sensitive to calcium hardness and are prone to form calcium phosphonate precipitates. There is thus a continuing need for safe and effective water treating agents which are sufficiently versatile to be used when substantial calcium and/or free chlorine is present in the water to be treated.